DE2643300A1 - ELECTRIC SWITCH ARRANGEMENT FOR AN ULTRASONIC PULSE ECHO METHOD FOR MEASURING THE WALL THICKNESS OF THE TEST PIECES - Google Patents

Description

2S4330Q

KRAUTKRÄMER GMBH '14-. September 1976

Luxemburger Str. 44-9 ^{IG / bö B} ^

5000 Cologne-4-1

Electrical circuit arrangement for an ultrasonic pulse echo method for measuring the wall thickness of the test pieces

The invention relates to a circuit arrangement for an ultrasound - Impulse echo method for measuring the wall thickness of test pieces, wherein an ultrasonic search signal is insonified into the test piece and a first and a second echo signal from the Test piece is received, wherein the second received signal has a lower amplitude than the first signal as well has a phase inversion to the first signal, with a receiver and an amplifier coupled to this, the output signals of which be fed to an electrical measuring device which measures time intervals.

It is already known from the transit time interval between entry echoes and back wall echo to determine the wall thickness of the test piece or the speed of sound in it. Here is the Thickness of the workpiece is equal to the product of the known speed of sound the ultrasonic wave, which travels through the workpiece, and half the measurement interval. However, two problems arise when measuring the wall thickness. The first problem is related to the attenuation of the ultra test signar

les along the sound path which the sound signal must occupy, i.e. along the thickness of the test piece. The other Problem relates to the phase difference between echo signals from the entry signal on the specimen surface and the back wall echo signal of the test piece depends. The signal weakening essentially depends on the microstructure and the porosity in the test piece. A circuit is already known . with a circuit controlling the amplifier output to combine to increase the gain of the receiver circuit, equal to or proportionate to that Thickness of the test piece. The use of the the reinforcement

controlling circuits improves the way it works visibly this weakening, however, here is the problem that Time interval errors due to the phase difference between these two signals cannot be eliminated.

The following must be taken into account here: If an ultrasonic signal hits on an acoustic discontinuity which is perpendicular to the signal path and gives rise to a higher acoustic impedance are the remaining areas of the signal path, part of the ultrasonic energy is reflected back to the transmitter probe in a known manner. In this ^ aIIe has the reflected signal a phase position which is the opposite of that of the insonified Signal is. If an ultrasonic signal hits an acoustic discontinuity with a lower acoustic impedance,

no phase reversal occurs. On the other hand, however, the signal which is reflected by the entry surface and the signal which is reflected by the rear wall of the test piece each have a phase difference of 180 ° to one another. With regard to the per se known relationship of the phase reversal, z. For example, reference is made to the book "Ultrasonics ¹¹ by D. Ensminger, Marcel Dekker, Inc., Uew Tork, 1973". An ultrasound device is also already known which has two complementary circles, one circle being a detector circle for the negative signal, the other is a detection circuit for a positive signal and must be used to process the phase difference between the entrance echo signal and the back wall echo signal. Here, a first, the negative signal dissipating detector circuit is used to produce an output pulse when the negative signal exceeds a first predetermined negative threshold value While a complementary, the positive signal dissipating detector circuit is used to emit an output pulse when the positive signal exceeds a second predetermined, but positive threshold value. The time interval between these two output pulses of the aforementioned detector circuits is known in a .. ι per se Measured way and further processed to indicate a measured quantity which is equal or proportionate to the thickness of the test piece.

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Now, however, the known detector circuits must be both in terms of phase negative as well as phase positive video signal. process, creating two amplifier control circuits become indispensable. One amplifier control circuit is assigned to each positive signal.

The invention has the object of providing an electrical switching arrangement which simplified training has, in particular, avoids two such detector circuits and two amplifier control circuits, although automatic monitoring of gain permits and a proper and optimal _e phase rotation. namely allow a rotation / 180 ° of the video signals due to acoustic discontinuities.

According to the invention it is provided that the phase of one of the electrical Signals that are based on an echo signal in the test piece are rotated by 180 °, so that two are based on echoes Signals with the same polarity are available for measurement purposes. Only one electrical circuit serves as a detector circuit and first receives the respective signals in positive and negative phase position. Through a video detector circuit is a signal is formed which indicates that a first video signal which is based on an echo signal has been received, this signal having an amplitude greater than that of a predetermined threshold value. This signal becomes a Triggered switch that causes the receiver to

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to rotate the phase of the subsequently received video signal by 180 °. "., Then the subsequently received, (widen. ·) Video signal in phase with the first video signal and the video detector circuit senses the subsequently received video signal when the amplitude exceeds the same predetermined threshold value. The electrical circuit also includes a automatic control means for the amplifier control, by which it is caused that the amplitude of the following Signals becomes equal to the predetermined amplitude. In this way the linearity of each signal becomes the same, so that the time interval measured between the successive signals that reach the predetermined threshold value, even then is fixed when the absolute value of the specified threshold value varies.

Embodiments of the invention are shown in the drawing and are explained in more detail below. Show it; Fig. Λ an electrical circuit arrangement, in simplified form

Block diagram, as a preferred embodiment. Figure 2 is a graph of the signal waveforms

for signals of the circuit according to FIG. 1. FIG. 3 shows an electrical, simplified circuit arrangement in a block diagram of another embodiment of the

Invention and
FIG. 4 shows, schematically and in a block diagram, an electrical circuit arrangement of a circuit part according to FIG.

1 and 3.

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According to FIG. T, output signals are periodically generated by the clock generator 12 fed to the input of the pulse generator circuit 10, the output of which with the input of the piezoelectric transducer or test head 16 is in communication. With every output signal of the Pulse generator TO sounds test head 16, which is attached to the test piece ¥ acoustically coupled via water, oil or some other means is, in each case an ultrasonic search signal in the test piece W.

If the ultrasonic signal hits an acoustic discontinuity, e.g. also on the surface 18 of the test piece, becomes a part the ultrasonic energy through the coupling means to the test head reflected. Here is the phase of the reflected signal phase shifted by 180 ° compared to the phase of the sounded signal. If the ultrasonic signal hits a second one acoustic imperfections, e.g. the rear wall19 of the test piece, becomes part of the sound energy through the test piece W and over the coupling means to the test head 16 is reflected. Here is the The phase of this echo signal is essentially equal to the phase of the sounded signalχ

In prop. 2, the track a is a graphic representation of the The waveform 60 represents echo signals received by the probe 16 corresponds to that which is reversed with regard to the phase position Echo signal that arises at the entrance surface while the Waveform 62: corresponds to the shape of the back wall echo. The waveform 62 has a phase rotation of 180 ° with respect to the

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Waveform 60 and a smaller amplitude that is due to the attenuation which the ultrasonic signal suffers when it traverses the thickness of the test piece ¥ twice.

In one of the above-mentioned known Hess circuits, the two video detector circuits were designed for threshold values of Y ~ "or V ^{+ in} order to measure the time interval between the points 64 and these signals originating from the echoes. A first electrical pulse was generated by the first tide detector when the signal resulting from waveform 60 became equal to or more negative than threshold V " at point 64; a second electrical pulse was generated by the second video detector when the signal associated with waveform 62 had a positive value equal to or greater than the threshold value V ⁺ at point 66. Then the time interval between this first and second pulse was measured by individually known circles, and a value corresponding to the thickness of the test piece was obtained.

In the embodiment according to the invention according to S ¹ Ig. 1, a signal is received by the single video detector circuit 22 which is equal to the time required for the ultrasonic beam to penetrate the thickness of the test piece. Clock generator 12 not only emits timing control signals to pulse generator circuit 10, but also a reset signal to flip-flop circuit 20 so that the flip-plop circuit does its job.

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can assume the starting position. If now the flip-flop! Reis 20 by it is triggered by a signal coming from the video detector circuit 22 changes his initial working condition, he gives Signal to the mixing circuit 24, so that the phase of the subsequently existing signals are rotated by 180 ° and the multiplex circuits 26 and 28 are caused to switch to their working state, as indicated below. There is also an automatic amplifier control circuit 30 (AGC) to control the Gain (amplitude gain) of the receiver circuit 14 to regulate automatically, so that the amplitude of each in the output located video signal, which is fed from the receiver circuit 14 to the mixer circuit 24, equal to a predetermined amplitude which is selected to prevent saturation of the elements in the circuit of FIG.

This control circuit 30 contains a programmable control generator 27 and a comparator element 29 · The voltage potential am Slider arm of the potentiometer 31 »one end of which to one The voltage source and the other end of which is grounded serves as the reference input value of the comparator 29 - that of the mixing circuit 24 incoming video signal is fed to the other input of the comparator. Whenever there is a signal in conductor 44 a smaller one than the voltage on the wiper arm of the potentiometer has, the power generator 27 is programmed to voltage over Conductor 32 to be fed to the multiplexer circuit 26. Is located the output signal of the flip-flop circuit 20 in its initial

state, the multiplex circuit 26 couples the control circuit 30 incoming current signal to the capacitance 34- and a buffer amplifier 36. The output of the buffer amplifier 36 is then over the multiplex circuit 28 is coupled to the receiver 14.

The receiver circuit is designed in such a way that it corrects the amplitude of the signal fed to the mixer 24 via conductor 42 can, in dependence on a voltage signal supplied from the multiplex circuit 28. The voltage of the control circuit 30 is selected so that the video signal fed to the Entrance surface decreases and is forwarded by the receiver 14, has a predetermined amplitude to saturation the mixing circuit 24 and the control circuit 30 to prevent.

If the signal from the video detector 22 forces the flip-flop circuit 20 to leave its initial state (flip-flop 20 is energized), the increased amplitude output signal from the AGC is generated by the signal fed via conductor 56 to the multiplexing circuit 26. Control circuit 30 coupled to capacitance 38 and buffer amplifier 40 in place of capacitance y \ - and amplifier 36, as indicated above. In the same way, the signal fed in via conductor 58 takes place via the multiplex. .r-Ereis 28 coupled the increased amplitude signal from the attenuator amplifier 40 to the receiver circuit 14. The gain of the receiver circuit 14, which depends on the amplitude of the signal coming from the MultiplexSireis 28, is increased so that

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a greater gain is available for the signal, which is based on that echo signal, its reflection. takes place from a discontinuity lying further away from the surface 18.

The video signals appearing in conductor 42 and onto the entrance surface as well as the rear wall echo decrease, have the same amplitude, but their phase position is 180 ° to each other turned. The phase of one of the video signals is rotated by 180 ° by the mixer circuit 24, as indicated above.

In a preferred embodiment of the invention, the Mixer circuit 24 as the variable gain component SG-3402 executed and a broadband amplifier / multiplier of commercial manufacture. Through this stage of the circuit is due to an incoming from the flip-flop circuit 20 via conductor 60 Signal, the input signal fed to the mixing circuit 24 via conductor 42 is rotated in phase by 180 ° and appears as such in conductor 44. Since the video signals supplied by receiver 14 via conductor 42 are of the same amplitude what is effected by the AGC control circuit 30 appear Signals in conductor 44 in the form shown in Fig. 2, trace b. Here the waveform 68 corresponds to the video signal, that goes back to the entry surface and through the receiver 14 is amplified and uses the voltage signal as the output voltage signal of the damper amplifier 36 back, which the

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Saturation of the mixing circuit 24 of the AGC control circuit 30 is prevented. On the other hand, the waveform JO corresponds to the video signal rotated by 180 ° in phase, which is due to the back wall echo, the rotation. by the mixing circuit 24, after amplification in the receiver circuit 14, and is based on the output voltage signal of the attenuator amplifier 40.

Operating sequence of the circuit according to FIG. 1. In operation, the clock generator 12 sends a signal to the pulse generator 10 and a reset signal to the flip-flop circuit 20 at the same time. The shifted to the zero position flip-flop circuit 20 forces the multiplex circuits 26 and 28 and the mixing circuit 24 to assume their initial states. Simultaneously with this, because the pulse generator 10 is coupled to the test head 16, the latter emits an ultrasonic search signal into the test piece W. As indicated above, the test head 16 also receives signals reflected from the test piece, here the input signal echo and the back wall echo, which have a phase shift of 180 but different amplitudes to one another, see FIG. 2, track a. The first echo signal is passed from the test head 16 to the receiver circuit 14 and is amplified here as a function of a voltage signal which comes from the attenuator amplifier J6. The video output signal from the receiver circuit 14 is fed via the conductor 42 to the mixer circuit 24; this mixer circuit 24 transmits the video signal, which has a waveform 60, via the line 44 without causing a phase shift. comes to the AGC tax

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circle 30 further, causes a signal amplitude by waveform 68 is shown and causes the transmission along the conductor 44, but now with a predetermined amplitude. Video detector 22 receives a video pulse and samples it, the pulse height being less than the predetermined threshold value V. is. By adjusting the sliding arm on potentiometer 52 the threshold voltage V can be readjusted or set. The potentiometer 52 has one end connected to a negative Voltage source, connected to earth at its other end. As indicated above, the AGC control circuit 30 provides a DC Eis signal to the multiplex old man 26. If now the first signal, represented by waveform 68, which is based on an echo signal, at voltage point 72 exceeds the voltage threshold V reached, the video detector emits a first pulse, energizes the flip-flop circuit 20 as well as a (not shown) transit time measuring circuit. The initial state of the flip-flop circuit changes, and he gives over the ladder 56, 58 and 60 from a signal which depends on the pulse emitted by the video detector 22, so that mixing circuit 24 is forced to use the Phase of the subsequently received video signals by "180 zu dre"., lien. . In addition, the status of the multiplex «: - Eceise 26 and 28 changed, now the output signal from the AGC control circuit 30 is applied to the input of the attenuator amplifier 40 (instead of the previous amplifier 36), and furthermore the output of the attenuator amplifier 40 via multiplex circuit 28 to the Recipient group 14 placed.

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The later echo echo signal in the mixing circuit 24 is thus um 180 rotated, and this phase shifted signal is supplied to the AGC control circuit 30. By the DC voltage signal from the control circuit 30 is the working voltage of the damper amplifier 40 changed, this voltage also via the multiplexer stage 28 is fed to the receiver circuit 14. The IComponentaides Control circuit 30 are selected so that they control the amplitude of the signal represented by waveform 70 as equal to the amplitude of the signal represented by waveform 68 regardless of the distance the ultrasonic echo signal wandered through in the test piece.

Now when the back wall echo signal (waveform 70) reaches the voltage threshold V at point 74-, it causes the video detector circuit 22 to form a second pulse, which flows to the transit time measuring circuit, so that the readiness to measure this Circle is ended. The time interval measured between the two pulses arriving from the video detector 22 is the same the thickness of the test piece.

The following advantage is also achieved here: The known measuring circuit has two video detectors, one with a negative voltage threshold V ~ and another with a positive voltage threshold V ⁺ and two AGC control circuits, one for the negative signals, the other for the positive signals. ! Do it can be seen that if either the positive or negative threshold

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value "V ⁺ or V ~, or both, have a deviation, which is due, for example, to the aging of its components, temperature changes or the like. The difference measurement is no longer accurate. In the circuit according to the invention, however, initially only one AGG control circuit JO is used because the two signals in the output of the mixer circuit 24- have the same polarity. Furthermore, the signals represented by the waveforms 68 and 70 essentially coincide because they have the same amplitude and phase, and therefore deviations or a fading phenomenon ( drift) at voltage threshold V do not enter into the time interval measurement, since a shift along waveform 68 to voltage point 76 is accompanied by an equal shift along waveform 70 to voltage point 78. Here it can be seen particularly clearly that the present invention is present thus, even fewer electrical components allow a more accurate thickness reading.

In the arrangement modifying the circuit arrangement according to FIG tion according to Figure 3, it is assumed that the receiver 14-the Fig./l must be able to gain from a first variable value which is used to amplify the input echo signal Ies ·, see waveform 60; e! Required, is, to a, second changeable · leim .. SferJ; - ax change, which is used to amplify the back wall echo signal, see waveform 62, is required. In itself, a group of recipients can As stated above, its dynamic range can be simplified and made cheaper. These

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according to the task is based on the circuit'Fig. 3 solved. Here is on Place of the receiver 14 · a receiver circuit 48 and an amplifier circuit 46 are used, both of which have limited dynamic range. The clock now sends 12 reset signals to the flip-flop circuit 20 and time pulses to the pulse generator circuit 10, so that through the test head 16 again periodic ultrasonic signals sounded into the test piece ¥. Again a potentiometer 50 is used, one end of which is connected to the voltage supply, the other end of which is connected to earth, with its wiper arm 54- with an input of the multiplex circuit 28 in Connection. The grinding arm 54- is adjusted so that the Power of the amplifier circuit 46 is set to a predetermined value. This causes the gain of the receiver circuit 48, depending on the output signal from the attenuator amplifier 40, which is dimensioned so that the amplitude of the video signal from the entrance surface is fed to the conductor 4-2 with a predetermined amplitude. When the entrance echo signal on the conductor 4-2 and thus on the conductor 44- less than or equal is the threshold value V, as determined by the setting on potentiometer 52, a pulse from video detector circuit 22 is the flip-flop circuit 20 supplied. In this case, the potentiometer 52 has a negative voltage at one end (the other End is earthed). The initial state of the flip-flop circuit is, as explained with reference to FIG. 1, changed. Attenuator amplifier 36 is now connected to amplifier circuit 46. Simultaneously third of the mixing circuit 24- the phase of the next

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incoming video signal, which is due to the back wall echo, by 480 °. The power of the amplifier circuits 4-6 is as indicated in Fig. 1 with reference to the recipient group 14-, changed .

The improvement of the circuit according to Pig. 3 consists essentially in that the gain of the recipient circle 4-8 and the Gain of the amplifier circuit 4-6 independently of each other or are adjustable. IEe verse tanking of the amplifier circuit 4-8 is changed depending on the input signal and the gain of the amplifier 4-6 depending on the back wall echo signal. In this way, the dynamic range of the amplifier circuit 4-6 is changed from a predetermined fixed value, which is determined by the position of the sliding arm 54- of the potentiometer 50 results, on a-Ji value, which is determined by the AGC-Sehleife, which includes the amplifier 36 is determined. The reinforcement of the receiver circuit 4-8 depends on the value, which is determined by the AGG loop, which the damper amplifier 4-0 contains and only has minor changes, so that only a smaller dynamic range for the recipient group 4-8 What is required: This makes the arrangement cheaper and simpler.

The above embodiments relate to a TJltrasonic thickness measuring device, with the distance between the entrance surface and back wall of the test piece is measured, however

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is the above teaching, as one of ordinary skill in the art will recognize, Also suitable for measuring the distance between two acoustic components, if the corresponding gate circles are connected to the video detector circle to be added.

Depending on the individual case, changes to the circuits are possible on the basis of the teaching according to the invention.

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Claims (6)

KRAUTKRÄMER GMBH September 14, 1976 IG / 13 ö B 091 PATENT CLAIMS J Circuit arrangement for an ultrasonic pulse echo method, for measuring the wall thickness or the speed of sound in test pieces, an ultrasonic signal being sounded into the test piece and a first and a second reflected echo signal being received, and the second signal having a lower amplitude than the first signal and for first signal is phase-shifted, with a receiver circuit and at least one Yerstärierkreis which is coupled to the receiver circuit, wherein the received and amplified signals are fed to a time-of-flight measuring circuit, characterized in that a phase reversal circuit is switched between receiver (14 ·, 4-8) and measuring circuit is that through it the amplified first echo signal is set to a predetermined value and furthermore an amplifier (30,36,40) which increases its output signal amplitude is separately coupled to the receiver circuit (14,4-8) and excites the receiver during the reception of the second echo signal so that this ", is also amplified to this predetermined amplitude and that .by receiver (14, 48) and phase reversal circuit only. the second echo signal] is reversed in phase relative to the first echo signal, so that both are fed to the measuring circuit with the same phase. 709315/0734 ORIGINAL INSPECTED 2. Circuit according to claim 1, characterized in that it has a detector circuit C 22), which of this circuit The signal formed depends on one of the echo signals which are brought to this predetermined amplitude. 3. A circuit according to claim 2, characterized in that the phase inversion circuit has a mixing circuit (24) whose input (at 60) with the output of the detector (22 ^), preferably via a flip-I? lop circuit (20), so that the signal phase is reversible. 4. A circuit according to claim 1, 2 or 3 »characterized in that its control part has an amplifier control circuit (30), the input of which is connected to the output of the phase reversal circuit (24 _r 22,60), so that the circuit (30) the The first echo signal and the second echo signal in the Biaoetingäcdrtes are fed that the input of a first multiplex stage (26) is coupled to the output of this amplifier control circuit (30), while the output of the first multiplex circuit (26) is coupled to the input of a first amplifier (36 ) is in communication, and that the input of a second multiplex circuit (28) is coupled to the output of the first amplifier (36) so that the output signal from the first amplifier (36) is fed to the amplifier (14, 48) adjust the subsequent signal of the first echo signal to a predetermined amplitude. 264330Q 5. Circuit according to one of claims 1-4, in particular according to claims 1-3, characterized in that the input of one second amplifier (40) is coupled to the input of a first multiplex stage (26), so that this amplifier (40), as a function of the signal generated by the detector circuit (22), an output signal (at 32) of the amplifier control circuit (JO) receives, and that the output of the second amplifier (40) with an input of the second multiplex circuit (28) is in communication, so that a signal, which is dependent on the signal formed by the detector (22), is sent to the receiver (48) is supplied, and that this signal is added to the second echo signal so that the latter to predetermined Amplitude is brought. 6. The method for using a circuit arrangement according to claim 1, characterized in that the control part of the circuit is designed so that the second echo signal is only reversed in phase after it 8.u £ has been brought to the predetermined amplitude. ? 09815/0784